As described in Patent Application WO2005028759A1, a building foundation structure is known having at least one through hole, and at least two connecting cables extending through and fixed to the structure, adjacent to the hole, and projecting upwards. When the foundation structure is completed, a metal foundation pile is inserted through the hole, is subjected statically to a series of thrusts to drive it into the ground, and, once driven in, the top part of the pile is fixed axially to the foundation structure. Each thrust is applied by a pile driver, which is positioned over the pile, cooperates with the top end of the pile, and is connected to the projecting part of the connecting cables, which, when driving the pile, act as reaction elements for the pile driver.
Alternatively, instead of the connecting cables, each hole in the foundation structure may be lined with a metal guide tube, which is fixed to the foundation structure by at least one ring embedded in the foundation structure, and has a top portion projecting upwards from the foundation structure and to which the pile driver is fixed rigidly.
As described in Patent Application WO2005028759A1, the pile driver is positioned over the pile to be driven, is connected to the projecting portion of the relative guide tube by at least two ties threaded at the top, and comprises at least one hydraulic jack comprising a cylinder and a piston movable axially with adjustable force with respect to the cylinder. The cylinder is placed on the top end of the pile, and the piston is brought into contact with the bottom surface of a reaction plate bolted integrally to the ties by respective bolts engaging the threaded top portions of the ties.
Once the pile driver is connected to the pile as described above, the hydraulic jack of the pile driver is activated to generate a force of given intensity between the jack cylinder and piston, and so subject the pile statically to a thrust, of the same intensity as the force, to drive the pile into the ground. The reaction force to the thrust exerted by the pile driver is provided by the weight of the foundation structure, and is transmitted by the ties, which, together with the guide tube, act as reaction elements, by maintaining the distance between the reaction plate and the foundation structure fixed as the piston comes out of the cylinder, thus driving the cylinder, and the top end of the pile with it, downwards.
The shaft of the pile driven into the ground is normally divided into a number of segments, which are driven successively, as described above, through the hole in the foundation structure, and are welded to one another. Once one shaft segment is driven, the pile driver is disconnected from the top end of the segment to insert another segment, which is butt welded to the driven segment; the pile driver is then connected to the top end of the next segment, and the driving cycle is continued.
The pile driver described above has several drawbacks: it takes a relatively long time to set up; it fails to provide for high driving force (over 75 tons); and it must be removed to join the driven shaft segment to the next segment.
U.S. Pat. No. 5,269,630A1 discloses an apparatus for lifting and stabilizing a structural slab overlying the ground including a base attached to the upper surface of the slab, at least one hydraulic cylinder vertically supported from the base, and a slip clamp assembly attached to the piston rod extending from the cylinder. Piling segments are sequentially passed downward through the slip clamp and through coaxial holes in the base and in the slab, and are driven into the ground by the hydraulic cylinder to form a support column under the slab.